Both packaging material and packages of the type described above are known in the art. For example, there occur on the market bottles which are produced by a combined extrusion/blow moulding operation of such triple-layer material. The material in these bottles has an interjacent or intermediate layer of High Density Polyethylene (HDPE) with admixed particles of carbon black and outer layers of HDPE on both sides of the interjacent layer.
The prior art bottles are employed, inter alia for transporting so-called UHT milk, i.e. milk which, for the purpose of extending its shelf life, has been subjected to a heat treatment at approximately 135-150° C. during approximately 1-2 seconds for reducing or eliminating the number of harmful micro-organisms occurring in the milk.
Since milk is a very light-sensitive product which do not stand lengthy exposure to light, in particular within the ultra violet wavelength range without being damaged, it is important that the milk is stored in its package in such a manner that it is not unnecessarily exposed to ultra violet radiation from its ambient surroundings.
Plastic layers consisting exclusively of HDPE are almost totally devoid of barrier properties against light, in particular ultra violet light, and consequently do not alone afford the light protection which is necessary in order for the milk to be able to be stored with the desired extended shelf life. In order to make the long-term storage of milk possible in the prior art bottles, particles of a light-absorbing material, normally carbon black, are therefore incorporated in the inteiacent layer of the packaging material, such particles efficiently absorbing, and thereby preventing impinging light from the outer ambient surroundings of the bottle from penetrating through the wall material of the bottle and reaching the packed milk.
However, particles of carbon black in the large quantities that are employed in the prior art packaging material make the interjacent layer extremely blackened, which could readily be seen through the outer HDPE layers of the bottle and give the bottle an unappealing black appearance if the interjacent layer were not concealed. In order to conceal the thus blackened interjacent layer, the outer HDPE layers of the bottle are therefore provided with a white colouring pigment of titanium dioxide, TiO2, in a sufficient quantity to conceal the black interjacent layer beneath and thereby impart to the bottle a more consumer-attractive white appearance.
However, the problem inherent in the prior art triple-layer material is that, as was mentioned above, it requires relatively large quantities of: the blackening particles of carbon black in the interjacent layer in order to attain the requisite light barrier properties, at the same time as it also requires correspondingly large quantities of white pigment (TiO2) in the outer layer for concealing the undesirable blackening caused by the particles. This entails unnecessary, but unavoidable, increased material consumption and thereby increased material costs for producing the material.
Another drawback which is related to the unnecessarily large quantity of carbon black particles is that the waste material which occurs in the bottle producing process cannot directly be recycled into the process because of the extreme blackening, but must first be whitened by the addition of white pigment (TiO2) or other white colouring matter in order to be able to be recycled and reused in the process. Such a handling involves extra material consumption and increased material costs, which often renders recycling and reuse unprofitable.